Iran has complied with an interim nuclear deal reached in 2013 with world powers by reducing its stockpile of low-enriched uranium gas, a UN report said July 1.

The International Atomic Energy Agency said in a confidential monthly report that Iran's stockpile of low-enriched gas was below a 7.6 ton ceiling set in the interim deal. That left it with several tons less of material that can be used to make atomic weapons.

U.S. officials touted the report as evidence that Iran is complying with the preliminary deal as talks in Vienna over a final deal enter the end stage.

But a U.S. think-tank questioned whether Iran had indeed complied with a second mandate in the interim deal to convert its low enriched uranium to a form with less proliferation risk, uranium dioxide.

The UN report "shows that only 9 percent of Iran's stockpile" had been converted that way, said the Institute for Science and International Security.

The group said "the United States revised its criteria for Iran meeting its obligations," when it became clear that Iran had not met this requirement.